The disclosure of Japanese Patent Application No. 2000-44708 filed in Feb. 22, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an apparatus for controlling valve timing of an internal combustion engine, which varies valve overlap in response to running conditions of the internal combustion engine.
2. Description of Related Art
Such a technology has been publicly known which achieves preferable performance of an internal combustion engine by controlling valve timing of an intake valve and an exhaust valve in response to running conditions of the internal combustion engine incorporated in a vehicle, etc. In such a technology, in order to take into consideration the combustion stability during the idling of an internal combustion engine, the combustion stability has been secured by lowering the amount of the remaining gas in a combustion chamber by preventing the valve opening periods of the intake valve and the exhaust valve from overlapping. (Japanese Patent Laid-Open Publication No. HEI 05-71369).
By controlling a valve timings of the intake valve and the exhaust valve so that such valve overlap is not produced in such an idling state, fuel that is injected through a fuel injection valve is adhered to an intake port and the inner surface of the combustion chamber when the engine is still cold, and the mixture becomes leaner than a predetermined air-fuel ratio, thereby causing the combustion to become unstable, wherein the drivability may be lowered due to cold hesitation.
Also, where the fuel injection amount is increased when cold in order to prevent such cold hesitation, the fuel efficiency and emission may be worsened.
The present invention was developed in order to solve the aforementioned problem. It is therefore an object of the invention to prevent the cold hesitation by suppressing becoming lean of the air-fuel ratio without increasing the fuel at cold idling.
In order to achieve the aforementioned object, one aspect of the invention is providing an apparatus for controlling the valve timing of an internal combustion engine, which varies valve overlap in response to running conditions of the internal combustion engine, wherein the valve overlap when cold idling is made larger than that when hot idling.
In the apparatus for controlling valve timing, when cold running, the valve overlap is made larger than that when hot running even in the case of idling. Fuel carburetion is increased in the combustion chamber and intake port due to blow-back of exhaust from an exhaust port and combustion chamber. Therefore, even if fuel injected from a fuel injection valve is adhered to the intake port and the inner surface of the combustion chamber when cold running, it is instantaneously carbureted. Accordingly, the mixture is subject to a sufficient air-fuel ratio without increasing the fuel supplied to the combustion chamber, wherein combustion will be further stabilized rather than in the case where the valve overlap is not increased, and cold hesitation can be prevented to maintain the drivability in a comparatively favorable state. Further, since the fuel does not have to be increased, it is possible to prevent fuel efficiency and emission from worsening.
Also, taking fuel stability into consideration when cold idling, the valve overlap is made smaller when hot idling than when cold idling. For example, an attempt was made so that the valve overlap does not occur. Therefore, the amount of the remaining gas in the combustion chamber is reduced, wherein it is possible to sufficiently stabilize the fuel.
In addition, in the apparatus for controlling valve timing, the valve opening period of both or any one of the intake valve and exhaust valve is controlled so that the valve overlap when cold idling is generated when an internal combustion engine is in cold idling, and no valve overlap is generated when hot idling thereof.
For example, by differently using the valve overlap in such cold idling and hot idling, the amount of the remaining gas is decreased when hot idling in which the fuel carburetion is sufficient, whereby an attempt is made so that the fuel stability becomes sufficient. And, when cold idling in which fuel carburetion is not usually sufficient, fuel is sufficiently carbureted due to blow-back of the exhaust to stabilize the combustion, thereby bringing about the aforementioned effect.
Another aspect of the invention is providing an apparatus for controlling valve timing, having a variable valve overlap mechanism that adjusts valve overlap by varying both or any one of the valve closing timing of an intake valve and the valve opening timing of an exhaust valve in an internal combustion engine and achieves valve overlap when cold running when the variable valve overlap mechanism itself does not operate.
The variable valve overlap mechanism is devised to be set to a timing that achieves valve overlap for cold running where the variable valve overlap mechanism itself does not operate. Therefore, even in a case where the variable valve overlap mechanism cannot be driven due to an insufficient output of oil pressure, etc., when cold running just after the starting of an internal combustion engine, the variable overlap mechanism is set to a valve timing that achieves valve overlap for cold running, before the starting of the internal combustion engine after the stop of the internal combustion engine. Therefore, in a situation such that the variable valve overlap mechanism does not sufficiently function when cold idling just after starting of the internal combustion engine, it is possible to achieve valve timing for cold running. It is possible to provide necessary valve overlap, for example, a state where no valve overlap is provided, and a state that larger valve overlap is secured than the valve overlap for cold running, since the valve overlap mechanism can be driven after the warm-up of the internal combustion engine.
Therefore, the mixture will have a sufficient air-fuel ratio without increasing the amount of the fuel into the combustion chamber when cold idling, and combustion can be stabilized still further than in the case of not increasing the valve overlap, and the cold hesitation can be prevented, wherein drivability can be maintained in a comparatively favorable state, and no increase in fuel consumption is required. The fuel efficiency and emission can be prevented from worsening. Accordingly, for example, when hot idling in which fuel carburetion is sufficient, the amount of the remaining gas in the combustion chamber is reduced, thereby achieving sufficient stabilization of combustion.
In addition, the variable valve overlap mechanism may be provided with one or both of an intake cam and an exhaust cam, whose profiles differ from each other in the rotation axis direction, a rotation direction shifter that can vary the valve overlap by consecutively adjusting the valve lift by adjusting the position in the rotation axis direction with respect to the cams whose profiles are different from each other in the aforementioned rotation axis direction, and a valve overlap setter for non-operation state, which when the variable valve overlap mechanism does not operate, sets the position of the cams in the rotation axis direction to the position corresponding to the valve timing at which the aforementioned valve overlap for cold running can be achieved.
The variable valve overlap mechanism is provided with one or both of an intake cam and an exhaust cam whose profiles differ from each other in the rotation axis direction. And, the cam is adjusted by the rotation axis direction shifter with respect to the position thereof in the rotation axis direction, whereby the valve lift is consecutively adjusted to enable consecutive changes in the valve timing.
And, when the variable valve overlap mechanism does not operate, the valve overlap setter for the non-operation state sets the position of the cam in the rotation axis direction to the position corresponding to the valve timing at which the valve overlap for cold running can be achieved.
In such a construction, in a case where the variable valve overlap mechanism cannot be driven due to the insufficient output of oil pressure, etc., when cold running after the starting of an internal combustion engine, the valve overlap setter for the non-operation state sets the position of the cam in the rotation axis direction to the position where the valve overlap for cold running can be achieved. Therefore, in a situation such that the variable overlap mechanism cannot be sufficiently driven when cold idling after the starting of the combustion engine, it is possible to achieve the valve overlap for cold running. Since the variable overlap mechanism can be driven after the internal combustion engine is warmed up, it is possible to achieve the required valve overlap, for example, a state in which the valve overlap is eliminated, or a state in which a valve overlap is secured that is larger than the valve overlap for cold running.
Accordingly, a mixture can be subject to a sufficient air-fuel ratio without increasing the fuel even when cold idling, and combustion is better stabilized than in the case of not increasing the valve overlap, wherein the cold hesitation can be prevented from occurring, and the drivability can be maintained at a comparatively favorable state. Further, fuel efficiency and emission can be prevented from worsening without requiring the fuel increase. Also, when hot idling where the fuel carburetion is sufficient, the amount of the remaining gas in the combustion chamber is reduced, thereby achieving sufficient stabilization of combustion.
In addition, the aforementioned cam is formed so that the valve lift may consecutively vary in the rotation axis direction. It may be shaped so that the valve overlap for cold running can be achieved at the position in the rotation axis direction where the valve lift assumes the minimum value.
According to such the cam, a thrust force acting in the direction along which the valve lift is decreased is generated at the camshaft by a pressing force from the valve lifter side which is brought into contact with the cam and causes the lift of the intake valve and exhaust valve to follow the cam surface. Therefore, when the variable valve overlap mechanism does not operate, it enters the most stabilized state such that the valve lifter is brought into contact with the position in the rotation axis direction, where the valve lift assumes the minimum value, in the position of the rotation axis direction.
Therefore, in a situation such that the variable valve overlap mechanism cannot operate sufficiently when cold idling after the starting of an internal combustion engine, since the valve lifter can function as a valve overlap setter for non-operation state, valve overlap for cold running can be naturally achieved. Since the variable valve overlap mechanism can be driven after the engine is warmed up, it will become possible to achieve the required valve overlap by the function of the rotation axis direction shifter, that is, it will become possible for the valve overlap to be eliminated, for example.
Further, the aforementioned valve overlap setter for non-operation state may be constructed as a rotation axis presser that makes the position in the rotation axis direction which has such a profile in which the valve lift is minimized, into a stabilized stop position when the cam is not driven.
By the rotation axis presser that makes the position in the rotation axis direction, which has such a profile in which the valve lift is minimized, into a stabilized stop position when the cam is not driven, the valve overlap setter for non-operation state may be achieved. In such a case, in a situation such that the variable valve overlap mechanism cannot be sufficiently driven when cold idling after the starting of an internal combustion engine, the rotation axis presser can achieve valve overlap for cold running. Since the variable valve overlap mechanism can be sufficiently driven after warm-up of the internal combustion engine, required valve overlap can be acquired against a pressing force of the rotation axis presser by the function of the rotation axis direction shifter, or the valve overlap can also be eliminated.
Further, the variable valve overlap mechanism enables adjustment of the valve overlap by varying a phase difference in rotation between the intake cam and exhaust cam of an internal combustion engine, and when the variable valve overlap mechanism itself is not driven, the aforementioned phase difference in rotation may become a phase difference in rotation, by which cold valve overlap can be achieved.
The variable valve overlap mechanism can adjust the valve overlap by varying the phase difference in rotation between the intake cam and exhaust cam. When the variable valve overlap mechanism is not driven, the valve overlap for cold running can be achieved by the phase difference in rotation.
Therefore, in the case where the variable valve overlap mechanism cannot be sufficiently driven due to an insufficient output of oil pressure, etc., when cold running after the starting of an internal combustion engine, the valve overlap mechanism has a phase difference in rotation to achieve cold valve overlap from when the engine stops to when the engine starts. Therefore, in a situation such that the variable valve overlap mechanism cannot be sufficiently driven when cold idling after the starting of an internal combustion engine, valve overlap for cold running can be achieved. And, since the variable valve overlap mechanism can be driven after warm-up of an internal combustion engine, and a phase difference in rotation can be adjusted, any required valve overlap can be secured, that is, it is possible to eliminate the valve overlap or to provide a larger valve overlap than the valve overlap for cold running.
For this reason, the mixture can be made into a sufficient air-fuel ratio without increasing the fuel when cold idling, and combustion is better stabilized than in the case of not increasing the valve overlap. As a result, cold hesitation can be prevented from occurring, and the drivability can be maintained in a comparatively favorable state. Furthermore, fuel efficiency and emission can be prevented from worsening, without requiring the increase in the fuel. The amount of the remaining gas in the combustion chamber is reduced when hot idling in which fuel carburetion is sufficient, and combustion can be better stabilized.
Still further, the variable valve overlap mechanism of an internal combustion engine may be provided with a rotation phase difference adjuster that is capable of adjusting the valve overlap by varying the phase difference in rotation between an intake cam and an exhaust cam, and a valve overlap setter for the non-operation state, in which, when the variable valve overlap mechanism is not driven, the phase difference in rotation between the intake cam and the exhaust cam by the aforementioned rotation phase difference adjuster is made into a phase difference in rotation by which valve overlap for cold running can be achieved.
In the variable valve overlap mechanism, when the variable valve overlap mechanism is not driven, the valve overlap setter for the non-operation state makes the phase difference in rotation between the intake cam and exhaust cam by the rotation phase difference adjuster into a phase difference in rotation at which valve overlap for cold running can be achieved.
In such a construction, even in a case where the variable valve overlap mechanism can not be sufficiently driven due to insufficient oil pressure, etc., when cold running after the starting of an internal combustion engine, the valve overlap setter for the non-operation state can bring about a phase difference in rotation, by which valve overlap for cold running can be achieved. Therefor, in a situation such that the variable valve overlap mechanism cannot be sufficiently driven when cold idling after the starting of the engine, it will become possible to achieve valve overlap for cold idling. Since the variable valve overlap mechanism can be driven after warm-up of the engine, it is possible to obtain the required valve overlap by the rotation phase difference adjuster. For example, valve overlap can be eliminated or a larger valve overlap can be obtained than the valve overlap for cold running.
Therefore, the mixture can be made into a sufficient air-fuel ratio without increasing the fuel when cold idling, and combustion is better stabilized than in the case of not increasing the valve overlap. As a result, cold hesitation can be prevented from occurring, and the drivability can be maintained in a comparatively favorable state. Furthermore, the fuel cost and emission can be prevented from worsening, without depending on an increase in the fuel. The amount of the remaining gas in the combustion chamber is reduced when hot idling in which fuel carburetion is sufficient, and the combustion can be better stabilized.
Still further, the variable valve overlap mechanism of an internal combustion engine may be provided with a rotation phase difference adjuster that is capable of adjusting valve overlap by varying the phase difference in rotation between an intake cam and an exhaust cam, and a valve overlap setter for the non-operation state, in which, the variable valve overlap mechanism is not driven after the cranking of an internal combustion engine, the phase difference in rotation between the intake cam and the exhaust cam by the aforementioned rotation phase difference adjuster is made into a phase difference in rotation, achieving valve overlap for cold running.
In the variable valve overlap mechanism, when the variable valve overlap mechanism is not driven after the cranking of an internal combustion engine, the valve overlap setter for the non-operation state makes a phase difference in rotation between the intake cam and exhaust cam by the rotation phase difference adjuster into a phase difference in rotation, by which the valve overlap for cold running can be achieved.
In such a construction, even in a case where the variable valve overlap mechanism can not be sufficiently driven due to an insufficient output of oil pressure, etc., when cold running after the starting of an internal combustion engine, the valve overlap setter for the non-operation state can already bring about a phase difference in rotation, achieving the valve overlap for cold running, till the cranking. Therefore in a situation such that the variable valve overlap mechanism cannot be sufficiently driven when cold idling after the starting of the engine, it will become possible to achieve the valve overlap for cold idling. Since the variable valve overlap mechanism can be driven after warm-up of the engine, it is possible to obtain the required valve overlap by the rotation phase difference adjuster. For example, valve overlap can be eliminated or a larger valve overlap can be obtained than the valve overlap for cold running.
Therefore, the mixture can be made into a sufficient air-fuel ratio without increasing the fuel when cold idling, and combustion is better stabilized than in the case of not increasing the valve overlap, wherein cold hesitation can be prevented from occurring, and drivability can be maintained in a comparatively favorable state. Furthermore, fuel efficiency and emission can be prevented from worsening, without depending on an increase in the fuel. And, the amount of the remaining gas in the combustion chamber is reduced when hot idling in which fuel carburetion is sufficient, and the combustion can be better stabilized.
A variable overlap mechanism of an internal combustion engine according to one embodiment of the invention comprises: one or both the intake cam and exhaust cam whose valve lifts consecutively varies in the direction of the rotation axis; a rotation axis direction shifter that is capable of varying the valve timing by consecutively controlling the valve lifts by adjusting the position in the direction of the rotation axis with respect to the aforementioned cam; a rotation phase difference adjuster that is capable of varying the phase difference in rotation between the intake cam and exhaust cam; and a coupler that couples the aforementioned rotation axis direction shifter and the aforementioned rotation phase difference adjuster with each other, and that, as the aforementioned cam moves to the position in the direction of the rotation axis where the valve lift is the minimum when the variable valve overlap mechanism is not driven, can achieve the valve overlap for cold running by varying a change in the phase difference in rotation between the intake cam and exhaust cam in synchronization with adjustment of the position of cams in the direction of the rotation axis by the aforementioned rotation axis direction shifter.
Thus, the variable valve overlap mechanism may be provided with both the rotation axis direction shifter and rotation phase difference adjuster. In this case, the rotation axis direction shifter is coupled with the rotation phase difference adjuster by a coupler. The coupler is constructed to vary a change in the phase difference in rotation between the intake cam and exhaust cam in response in synchronization wiht the adjustment of the position of cams in the direction of the rotation axis by the rotation axis direction shifter. By this, as the cams move to the position in the direction of the rotation axis where the valve lift assumes the minimum value when the variable valve overlap mechanism is not driven, the valve overlap for cold running can be achieved by the movement.
In such a construction, even in a case where the variable valve overlap mechanism cannot be driven due to an insufficient output of oil pressure, etc., when cold running after the starting of an internal combustion engine, the valve overlap for cold running can be achieved by the coupler. And, since the variable valve overlap mechanism can be produced after the engine is warmed up, required valve overlap can be brought about by one or both of the rotation axis direction shifter and rotation phase difference adjuster. For example, no valve overlap is provided, or a larger valve overlap than the valve overlap for cold running can be achieved.
Therefore, the mixture can be made into a sufficient air-fuel ratio without increasing the fuel when cold idling, and the combustion is better stabilized than in the case of not increasing the valve overlap, wherein cold hesitation can be prevented from occurring, and the drivability can be maintained in a comparatively favorable state. Furthermore, the fuel cost and emission can be prevented from worsening because the increase in the fuel is not required. The amount of the remaining gas in the combustion chamber is reduced when hot idling in which fuel carburetion is sufficient, and the combustion can be better stabilized.
The aforementioned coupler is caused to move in the direction along which the phase difference in rotation between the intake cam and exhaust cam makes the valve overlap smaller in response to an increase in the valve lift by adjusting the position of the cams in the direction of the rotation axis by the rotation axis direction shifter, by coupling the rotation axis direction shifter and the rotation phase difference adjuster with each other by a helical spline mechanism.
Thus, the coupler is provided with the helical spline mechanism that connects the rotation axis direction shifter to the rotation phase difference adjuster. In the helical spline mechanism, the phase difference in rotation between the intake cam and exhaust cam makes the valve overlap become smaller in response to an increase in the valve lift by adjusting the position of the cam in the rotation axis direction by the rotation axis direction shifter. That is, it is devised that the valve overlap is made larger in response to the valve lift becoming smaller.
Therefore, by a thrust force generated by a pressing force of a valve lifter that is brought into contact with the cam and that causes the lift of the intake valve and exhaust valve to follow the cam surface, it enters the most stabilized state such that the valve lifter is brought into contact with the position in the direction of the rotation axis where the valve lift assumes the minimum value in the position in rotation axis direction when the variable valve overlap mechanism is not driven. As the valve lift is adjusted to the minimum value, the phase difference in rotation between the intake cam and exhaust cam is adjusted by the helical spline mechanism so that the valve overlap becomes large, achieving valve overlap for cold running.
Therefore, under the situation that the variable overlap mechanism cannot be sufficiently driven when cold running after the starting of engine, it is possible to naturally achieve the valve overlap for cold running. Since the variable valve overlap mechanism can be driven after the engine is warmed up, it is possible to achieve the required valve overlap by the functions of the rotation axis direction shifter and rotation phase difference adjuster, and for example, the valve overlap can be also eliminated.
Also, an apparatus for controlling valve timing in an internal combustion engine according to one embodiment of the present invention may be provided with: a variable valve overlap mechanism for an internal combustion engine; a running status detector for detecting the running state of the internal combustion engine; and a valve overlap controller that, in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates cold idling, can maintain the valve overlap for cold running, which is achieved when the variable overlap mechanism is not driven before the starting of the internal combustion engine, and in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates hot idling, can eliminate any valve overlap or employ valve overlap which is smaller than the valve overlap for cold running, by driving the variable valve overlap mechanism, and in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates a hot non-idling state, can employ valve overlap larger than the valve overlap in the aforementioned hot idling state by driving the variable valve overlap mechanism.
The valve overlap mechanism maintains valve overlap for cold running, which is achieved when the variable valve overlap mechanism is not driven before the starting of an internal combustion engine in a case where the running status of the internal combustion engine, which is detected by the running status detector, indicates cold idling. Also, it eliminates the valve overlap by driving the variable valve overlap mechanism or adjust to the valve overlap for hot running, which is smaller than the valve overlap for cold running, in a case where the running status of the internal combustion engine, which is detected by the running status detector, indicates hot idling. Still further, the variable valve overlap mechanism employs valve overlap which is larger than the valve overlap for hot idling by driving the variable valve overlap mechanism in a case where the running status of the internal combustion engine, which is detected by the running status detector, indicates hot non-idling.
Thereby, the mixture will have a sufficient air-fuel ratio without an increase in the fuel when cold idling, and the combustion can be stabilized still further than in the case of not increasing the valve overlap, and the cold hesitation can be prevented, wherein the drivability can be maintained at a comparatively favorable state, and no increase in fuel consumption is required. The fuel cost and emission can be prevented from worsening. Accordingly, for example, when hot idling in which fuel carburetion is sufficient, the amount of the remaining gas in the combustion chamber is reduced, and the combustion can be sufficiently stabilized.
In addition, an apparatus for controlling valve timing in an internal combustion engine according to one embodiment of the invention, may be provided with: a variable valve overlap mechanism for an internal combustion engine; a running status detector that detects the running state of the internal combustion engine; and a valve overlap control device that, in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates cold idling, can maintain the valve overlap for cold running, which is achieved when the variable overlap mechanism is not driven before the starting of the internal combustion engine, and in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates other hot states, can employ valve overlap responsive to the running status of the internal combustion engine by driving the aforementioned variable valve overlap mechanism.
The valve overlap control device can maintain the valve overlap for cold running, which is achieved when the variable overlap mechanism is not driven before the starting of the internal combustion engine in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates cold idling, and can employ a valve overlap responsive to the running status of the internal combustion engine by driving the aforementioned variable valve overlap mechanism in the case where the running status of the internal combustion engine detected by the aforementioned running status detector indicates other hot states.
Therefore, the mixture can be made into a sufficient air-fuel ratio without increasing the fuel when cold idling, and combustion is better stabilized than in the case of not increasing the valve overlap, wherein cold hesitation can be prevented from occurring, and the drivability can be maintained in a comparatively favorable state. Furthermore, fuel efficiency and emission can be prevented from worsening, without depending on an increase in the fuel. And, the amount of the remaining gas in the combustion chamber is reduced when hot idling in which fuel carburetion is sufficient, and combustion can be better stabilized.
The embodiment of the invention is not limited to the apparatus for controlling valve timing as described above. Another embodiment of the invention is, for example, a vehicle in which an apparatus for controlling valve timing is incorporated, and it relates to a method for controlling valve timing of an internal combustion engine.